1. Field of the Invention
The present invention relates to a magnetic thin film containing an alloy of a L11 type atom ordered structure. In more detail, the present invention relates to a magnetic thin film achieving a magnetic characteristic excellent due to the structure. The present invention relates to a method of manufacturing such magnetic thin film, and various application devices using the magnetic thin film.
2. Description of the Related Art
Various devices using a magnetic thin film include a magnetic recording medium, a tunnel magnetic resistive element (TMR), a magnetic resistive random access memory (MRAM), a micro-electromechanical system (MEMS) device, and the like.
First, the magnetic recording medium will be described as an example of the various devices using the magnetic thin film. The magnetic thin film is used in a magnetic recording device such as a hard disc, an optical magnetic record (MO), and a magnetic tape, and the magnetic recording system includes an in-plane magnetic recording system and a perpendicular magnetic recording system.
The in-plane recording system is the conventional system, for example, a system for carrying out a magnetic record horizontal to a hard disc surface. However, in recent years, there is mainly used the perpendicular magnetic recording system which can achieve a higher record density by carrying out the magnetic record perpendicular to the disc surface. Various studies have been made on a medium (perpendicular magnetic recording medium) to which the perpendicular magnetic recording system is applied, and for example, the following technology is disclosed.
Japanese Patent Laid-Open No. 2006-85825 discloses a perpendicular magnetic recording medium provided with a granular structure where at least an under layer, a magnetic layer and a protective layer are sequentially formed on a substrate, wherein the magnetic layer comprises ferromagnetic crystal grains composed essentially of a Co—Pt alloy and non-magnetic grain boundaries composed essentially of an oxide surrounding the crystal grains, and wherein the under layer comprises an alloy of two or more elements of any of Cu, Pd and Au or any of Cu, Pd, Pt, Ir and Au. The perpendicular magnetic recording medium has excellent low noise characteristics, thermal stability and writing characteristics, and is capable of performing high density recording and being manufactured at a low cost.
At present a crystalline film of a Co—Pt alloy is mainly used in the magnetic layer of the perpendicular magnetic recording medium. The crystalline film of the Co—Pt alloy has a crystal orientation so controlled that a C axis of a Co—Pt alloy with a hexagonal closest packed structure (hcp) is perpendicular to a film plane (that is, C plane is parallel to the film plane), thereby enabling the perpendicular magnetic recording.
As one system for controlling magnetic characteristics of the magnetic layer, there is known a system for forming a granular magnetic layer having a structure of surrounding a periphery of the ferromagnetic crystal grains by a non-magnetic and non-metallic substance such as an oxide and a nitride.
In the granular magnetic layer, the grain boundary phase of the non-magnetic and non-metallic substance physically separates the ferromagnetic grains. Therefore, since a transition region of recording bits is narrowed without excessively increasing a magnetic mutual operation between the ferromagnetic grains to restrict the fluctuation, low noise characteristics can be obtained.
In recent years, in order to reduce a magnetic influence with each other between adjacent tracks for the purpose of realizing a higher recording density in the perpendicular magnetic recording medium, development of discrete track media (DTM) where a groove is formed between the tracks has been actively made. In addition, for enabling recording of one bit per one magnetic dot (or one magnetic grain), development of bit pattern media (BPM) where magnetic dots (or magnetic grains) are also artificially orderly lined up has been actively made.
Further, for obtaining a perpendicular magnetic recording medium capable of carrying out recording on a magnetic film having a high holding magnetic force, there is proposed a thermal assist magnetic recording (HAMR or TAMR) system, an energy assist recording system (MAMR) by a micro wave, or the like, and studies on the magnetic recording medium using these recording systems also have been actively made.
Next, a tunnel magnetic resistive element (TMR) as another example of various devices to which the magnetic thin film is applied and a magnetic resistive random access memory (MRAM) using the tunnel magnetic resistive element will be described. The conventional memory such as a flash memory and a dynamic random access memory (DRAM) records information using electrons in the memory cell, but MRAM is a memory using the same magnetic element as the hard disc in a recording medium.
MRAM has address access time of about 10 ns and cycle time of about 20 ns. Therefore, reading and writing by MRAM can be made at a high speed about five times the speed of DRAM, that is, substantially the same as a static random access memory (SRAM). In addition, MRAM has an advantage that low consumption power of about 1/10 of the flash memory and high cumulative performance can be realized.
Here, TMR used in MRAM can be constructed, for example, of a laminated element in which a ferromagnetic thin film is formed on an anti-ferromagnetic thin film, and various technologies are disclosed in relation thereto.
Japanese Patent Laid-Open No. 2005-333106 discloses an exchange-coupled element in which an anti-ferromagnetic layer and a ferromagnetic layer exchange-coupled to the anti-ferromagnetic layer are sequentially laminated on a substrate, and the anti-ferromagnetic layer has an order phase of a Mn—Ir alloy (Mn3Ir). FIG. 5 in this document discloses a schematic cross section of TMR. FIG. 4 in this document discloses a spin valve type magnetic resistive element equipped with the exchange coupled element, and this element is also a laminated element in which a ferromagnetic thin film is formed on an anti-ferromagnetic thin film in the same way as TMR described above.
Further, a micro electromechanical system (MEMS) device will be described as another example of the various devices to which the magnetic thin film is applied. The MEMS device is a generic name of a device in which mechanical element components, sensors, actuators, and/or electronic circuits are integrated on one silicon substrate, one glass substrate, one organic material or the like. Application examples of the MEMS device may include a digital micro mirror device (DMD) which is one kind of an optical element in a projector, a micro nozzle used in a head portion of an ink jet printer, various sensors such as a pressure sensor, an acceleration sensor and a flow sensor, and the like. These devices will hopefully be applied to not only manufacturing industries but also a medical field.
In any of the various devices (magnetic recording medium, TMR, MRAM, and MEMS device) to which the magnetic thin film is applied shown above, an improvement on magnetic characteristics of the magnetic thin film, specially the uniaxial magnetic anisotropy (Ku) is demanding. Development of the magnetic thin film showing such an excellent Ku value is considered to contribute greatly to a large capacity process and/or a high density process of a recording medium and a memory.
For example, as a magnetic recording layer of the perpendicular magnetic recording medium, a recording layer equipped with grains or dots having a structure in which a hard magnetic layer and a soft magnetic layer are laminated, such as an ECC (exchange coupled composite), a hard/soft stack and an exchange spring is proposed as means for achieving the high density process.
However, for sufficiently effecting characteristics of these media to realize high thermal stability and excellent saturation recording characteristics, it is necessary to use the perpendicular magnetization film showing a large Ku value of the order of 107 erg/cm3 in the hard magnetic layer.
In addition, also in MRAM of a spin injection magnetization reverse type expected as the future high density memory, there have been made studies on realization of a large capacity process by using the perpendicular magnetization film showing a large Ku value of the order of 107 erg/cm3.
There have been made various studies on the perpendicular magnetization film showing a Ku value suitable for being used in such a magnetic recording medium and memory, and for example, the following technology is disclosed.
In H. Sato, et al., “Fabrication of L11 type Co—Pt ordered alloy films by sputter deposition”, J. Appl. Phys., 103, 07E114 (2008), manufacture of L11 type Co—Pt ordered alloy films by sputter deposition is disclosed. In addition, in S. Okamoto et al., “Chemical order-dependent magnetic anisotropy and exchange stiffness constant of Fe—Pt (001) epitaxial films”, Phys. Rev. B, 66, 024413 (2002) and Japanese Patent Laid-Open No. 2004-311925, L10 type Fe—Pt ordered alloy films are disclosed. Further, in Japanese Patent Laid-Open No. 2002-208129, Japanese Patent Laid-Open No. 2003-173511, Japanese Patent Laid-Open No. 2002-216330, Japanese Patent Laid-Open No. 2004-311607, Japanese Patent Laid-Open No. 2001-101645, and Patent Publication No. WO2004/034385, L10 type Fe—Pt ordered alloys such as a Fe—Pt ordered alloy, a Fe—Pd ordered alloy and a Co—Pt ordered alloy, and a magnetic recording medium using this as a magnetic layer are disclosed. It should be noted that the L11 type Co—Pt ordered alloy films disclosed in H. Sato, et al., “Fabrication of L11 type Co—Pt ordered alloy films by sputter deposition”, J. Appl. Phys., 103, 07E114 (2008) can realize a much larger order degree as compared to the conventional alloy film, which is therefore expected to show a remarkably large Ku value.
However, under recent situations in need of a large capacity process and a high density process of various devices, it is desired to develop a perpendicular magnetic recording layer (magnetic thin film) having uniaxial magnetic anisotropy in size equal to or more than any magnetic thin film disclosed in the above documents and capable of being formed by a simpler manufacturing technology.
Accordingly, an object of the present invention is to provide a magnetic thin film having large uniaxial magnetic anisotropy, a method of manufacturing the magnetic thin film, and various application devices using the magnetic thin film.